Expandable drill bit

A drill bit system comprising a rotating device, a support string and an expandable drill bit which are coupled together, wherein the expandable drill bit comprises:

• a body mounted on the support string,
• a plurality of drill arms coupled to the body and extending along a central longitudinal axis, at least one drill arm supporting cutting elements,
• the plurality of drill arms are pivotable between a retracted configuration and an expanded configuration, the retracted configuration defining an expandable drill bit having a first cutting diameter, the expanded configuration defining an expandable drill bit having a second cutting diameter greater than the first cutting diameter, and
• wherein the arms are driven from the retracted configuration into the expanded configuration when the rotating devices rotates the expandable drill bit at a speed of rotation at least equal to a determined expanding speed of rotation, and wherein:
• the drill arms comprise at least two main drill arms, and at least two intermediate drill arms, the main drill arms defining an end of a drill bit internal conduit coaxial to the central longitudinal axis,
• in the retracted configuration, each main drill arm contacts another main drill arm, and the intermediate drill arms are positioned within the end of the drill bit internal conduit, and
• in the expanded configuration, the main drill arms and the intermediate drill arms pivot laterally so that each intermediate drill arm fits between two main drill arms.